Thanks for the replies.  I've run Holley vacuum secondary 600s for years on everything from 289s to 427s. I'm not familiar with anything smaller. My car will not be a daily driver.  I'll only drive it to car shows and lunch once in a while.  As soon as I get the 292 sorted out, I'm going to build a better short block with small popups, an Isky cam and tube headers.  Also my car has a manual transmission with OD and the rear end ratio is lower.   I get the throttle response issue, especially with an automatic. 

These non-race Y-motors are mostly used for torque application on street machines - where throttle response is going to be more appreciated than gross CFM numbers. The 390 cfm carbs fill the bill for about 80%- 90% of our street applications - so does the 465 cfm. We've got owners of more daily driver sort of vehicles than anything else on here.

 
 Steve Metzger       Tucson, Arizona

I prefer the 390 cfm on stock engines, I've had good  performance and economy. The 390 type have smaller venturi bores which better match the Y manifold. Using larger carbs requires machining the manifold if you do it correctly.
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Carburetor size is not that critical for a 292-312 to worry about.  A 600 cfm carburetor will work just fine on a healthy engine.  In actuality it should be more fuel efficient since the primary throttle bores will typically be smaller than an Autolite 2V, or Holley 2V.  I would not be against using an even larger carburetor on a higher compression, and fresh build engine with headers and dual exhausts.  Better to be slightly larger than needed than too small unless you are looking for economy, not performance.  Joe-JDC

JDC

Ive tried a 450 and a 600 Holley and played with them a bit and I found no great difference between them to be honest. Im currently running a 1406  600 Edelbrock  with a few minor tweaks and I think I might have just a tiny bit more mid range ...  



"Came too close to dying to stop living now!"

Praise not precise....damn computers.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

All of the Summit carbs get high precise here and by yBlock owners.

Holley offers # 1848-1 a 465 cfm carb not known to many. It is used on rock crawlers with Excellant off idle throttle responce which is what they require. Funny that if you bring up this on the Holley web page it shows Ford style linkage and not your typical GM which makes for a clean installation.

The Holley "Brawler" series offers the 570cfm.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

In general using a larger carb than necessary will reduce the responsiveness of the engine and could present other tuning difficulties.  That said, you do want to err on a vacuum secondary carb being a little bigger than needed.  Key words are "a little."

If you are nearly certain that you will build a modified motor, get the 600.  I suggest the Street Avenger series, which would be 570, because it is a more modern carb and you get some good features for the money.  If an engine build is something that you are merely tossing around as an idea, get the 450 as it will be more than needed for your motor.  Another thing to consider is depending on your future engine build, the 600 may actually be too small.  That's just another reason that it is best to pick a carb for what you have now rather than what you think you might have in the future.

You should also consider the Summit Racing branded carburetors which are available in 500, 600, and 750cfm sizes.  You get a lot for the money with those carbs.


Lawrenceville, GA

If You want a real nice running Carb for stock Engine a 8007-0 390 CFM Holley works well. IMO a 600 is too big. 

  

I will be upgrading the Tea Pot Carb and Load-A-Matic Distributor on my 55 Bird.   I will be installing a 1957 distributor with a Pertronix unit.  I have a set of reconditioned 1957 G Heads and an iron 1957 Ford Holley pattern intake also.  I need to purchase a Holley Carb for this intake.  I am thinking about buying a new 600 cfm Holley with vacuum secondaries.  I see on this forum where some of you are running a 450 cfm carb.   My engine is stock, but I probably will want to build a mildly modified engine in the future.  Is there any advantage or disadvantage to purchasing a 600 cfm Holley?